Software synchronization of multiple scanning probes

ABSTRACT

A method and apparatus for scanning multiple scanning probe microscopes in close proximity, to scan overlapping scan areas at the same time while avoiding collision employs a control system providing drive signals to a first Atomic Force Microscope (AFM) and calculated drive signals to additional AFMs based on the first drive signals and the relative position of the additional AFMs to the first AFM for consistent spaced motion. Scanning and Failure Analysis (FA) probing of multiple feature of interest using multiple APMs allows for reduced time for locating FA features to set up measurements.

RELATED APPLICATION

This application claims priority to U.S. provisional application Ser.No. 60/394,414, filed Jul. 8, 2002, and is a continuation of U.S. patentapplication Ser. No. 10/615,223 filed Jul. 7, 2003 now U.S. Pat. No.6,880,389, both entitled “Software Synchronization of Multiple ScanningProbes”, the disclosures of which are fully incorporated herein byreference.

COPYRIGHT NOTICE

Certain software programs or routines disclosed in this application aresubject to copyright protection and all rights thereto are specificallyreserved. No dedication to the public of those copyrights is intended ormade by such disclosure in this specification.

BACKGROUND

1. Field of the Invention

This invention generally relates to scanning probe microscopy (SPM) andfailure analysis (FA), and more specifically to a system of control ofmultiple probe scanning when SPM is used to locate features for FA.

2. Description of the Related Art

Location of features in semiconductor microcircuits for failure analysis(FA) work has often been a difficult task. With advancing technology thesize of features of interest for FA has decreased. Traditional methodsof making electrical contact to features of interest in FA, also calledprobing, involved using mechanical positioners with fine probing needlesand an optical microscope. The positioners are precision, 3-axis stagesthat can be manual or motorized. Attached to the positioners are sharp,probing needles. Using a traditional optical microscope and thepositioner, a user would probe the FA device of interest with theneedle. The small size of current semiconductor technology has madelocation and probing of FA features difficult or even impossible becauseof the limits of optical microscopy.

Scanning probe microscopy (SPM) is one technique that can be used tolocate these features. SPM can be used to create and image and locatefeatures of interest that are much smaller than features that could belocated using traditional optical microscopy. Since SPM can probe onlyone FA feature of interest per scanning probe microscope, multiplescanning probes are needed to contact multiple features. The field ofusing SPM, also called Atomic Force Microscopy (AFM), for the purpose ofFA probing is called Atomic Force Probing (AFP). The acronym AFP is usedto describe the field as well as instruments designed for use in thefield, Atomic Force Probes.

The prior art contains many examples of using SPM to locate FA featuresincluding using a single SPM to locate FA features. However, only alimited number of FA experiments can be performed with a single probe asmany devices of interest for FA require 2 probes, in the case of diodes,3 probes, in the case of transistors, or even more probes.

The limited prior art relating to multiple scanning probes for FA showsthe probes scanning one at a time in order to avoid collisions. Thismethod is effective at avoiding collisions, at least until the probesmove to their respective features of interest. However, this methodtakes longer to perform the scanning. This allows more time for drift,such as thermal drift, to occur. Also, the simple fact of longermeasurement time is a serious weakness of the prior art.

One embodiment of the prior art for 2 probes is shown pictographicallyin FIGS. 1 a-1 d. A sample 110 contains features of interest 112. Thesefeatures of interest 112 may be too small to be probed easily usingtraditional methods. FIG. 1 a shows the scanning probe tips 114 grosslypositioned on the sample 110 and near the features of interest 112. Eachscanning probe tip 114 will scan and image a scan area 116. FIG. 1 bshows the first scanning probe tip 114 starting at a start point 118 andscanning its area of interest 116. FIG. 1 c shows the same process forthe second scanning probe tip 114. At any given point during scanningthe scan direction 120 for the different scanning probe tips 114 may ormay not be the same direction. FIG. 1 b and FIG. 1 c show differentscanning directions, as is common in the prior art. FIG. 1 d shows thescanning probe tips 114 positioned on the features of interest 112 andready for an FA experiment. This process took twice the amount of timeas was required for one scan. Similarly, if more probes are needed inthe experiment the time delay scales with the number of probes used.

This process also requires a difficult initial gross positioning setup.When the scanning probes tips are initially placed, they must besufficiently far apart so that when one scanning probe tip is scanning,it does not collide with any other scanning probe tip that is notscanning. This requires initially placing the scanning probe tipssufficiently far apart to avoid the collision, and makes placing thescanning probe tips sufficiently close together to scan and image thesame area difficult.

It is, therefore, desirable to perform SPM using multiple probes andprovide scanning of multiple probes in the same amount of time as wouldbe taken to perform a scan of a single probe. This provides theadvantage of less time for SPM drift effects, as well as the simpleadvantage of less measurement time. This also provides the advantage ofa more simple and efficient initial gross positioning setup, becausecollision with scanning probe tips that are not scanning does not needto be avoided.

SUMMARY OF THE INVENTION

A device and method to simultaneously scan multiple scanning probes overoverlapping or non-overlapping areas of interest to locate respectivefeatures of interest in a minimum amount of time employs at least twoscanning probes, each probe supported by cantilever to an atomic forcemicroscope (AFM). A controller in each AFM receives motion controlsignals from a master controller generating a first motion controlsignal for a first one of the AFMs for motion in a first axis and asecond motion control signal for the first AFMs for motion in a secondaxis. The second axis is substantially perpendicular to the first axis.The master controller then calculates a first offset motion controlsignal responsive to the first motion control signal for a second one ofthe AFMs for motion in spaced relation to the first one of the AFMs inthe first axis and a second offset motion control signal responsive tothe second motion control signal for a second one of the AFMs for motionin spaced relation to the first one of the AFMs in the second axis.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will bebetter understood by reference to the following detailed descriptionwhen considered in connection with the accompanying drawings wherein:

FIGS. 1 a to 1 d depict prior art technique of scanning multiplescanning probes one after another to scan and probe features ofinterest;

FIGS. 2 a to 2 c depict employment of an embodiment of the presentinvention for scanning multiple scanning probes simultaneously to scanand probe features of interest;

FIGS. 3 a to 3 c depict an embodiment of the present invention for 3probes;

FIG. 4 shows three scanning probe tips and the sample, as viewed fromthe top;

FIG. 5 a is a block diagram of the hardware configuration of anembodiment of the invention;

FIG. 5 b is a detailed side view of an embodiment of the probe tip andcantilever FIG. 6 a is a flow chart for software implementation ofcertain control aspects for an embodiment of the invention;

FIG. 6 b is a continuation of the flow chart of FIG. 6 a;

FIGS. 7 a to 7 f are schematic representations of some of the electricalwaveforms in the embodiment described;

FIGS. 8 a to 8 c show employment of an embodiment of the presentinvention scanning multiple scanning probes simultaneously to scan andprobe features of interest while avoiding a certain area;

FIG. 9 is a flow chart for the software implementation of the Z axiscontrol for area avoidance; and,

FIGS. 10 a to 10 c show waveforms representative of the control signalsfor the control routine defined in FIG. 9.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIG. 2 a, an embodiment of the present invention employs twoor more scanning probe tips 114 a and 114 b that are located near asample 110. The sample 110 contains the features of interest 112 a and112 b. FIG. 2 b shows the scanning probe tips in relation to desiredscan areas 116 a and 116 b respectively. Note that in the embodimentshown, the scan areas 116 a and 116 b are overlapping. Each scan areahas a start point 118 a and 118 b where the respective scanning probetip will begin its scan. Each scanning probe tip also has a scandirection 120 a and 120 b respectively. In the embodiment shown the scandirections 120 a and 120 b are always parallel and offset for allscanning probe tips. This provides for simultaneous motion of the probetips in spaced relation thereby avoiding collision. FIG. 2 c shows thescanning probe tips positioned on the features of interest and ready foran electrical measurement or force measurement.

FIGS. 3 a, 3 b and 3 c show an embodiment of the invention adding athird probe 114 c for simultaneously scanning a third desired scan area116 c. A third feature of interest 112 c is also depicted.

FIG. 4 shows the geometrical relationship of three scanning probe tips114 a, 114 b and 114 c positioned over the sample 110. The scanningprobe tips are at different angles from one another. The platen angle122 a, 122 b and 122 c of scanning probe tips 114 a, 114 b and 114 c,respectively, is the angle of the probe centerline 124 a, 124 b and 124c, respectively, as measured from a reference axis 126. Each scanningprobe tip has a unique platen angle. The present invention employs theplaten angle for the probe tips for generation of control signals aswill be described in greater detail subsequently.

FIG. 5 a shows a schematic diagram of the elements of an AFP systemembodying the present invention. The user accesses the software via acomputer 130. The computer is of a standard configuration, such that itis connected to a screen 132, a mouse 134, and a keyboard 136. The scanimage 137 is displayed on the computer screen. The computer 130generates scan waveforms 138 a, 138 b and 138 c. A generalized case formore than three probes is represented by waveform 138 i. The generationof the scan waveforms is described subsequently with respect to FIG. 6.There is one complete, independent set of scan waveforms to controlmotion of a probe tip for each feature of interest 112. The scanwaveforms are output to digital to analog converters (DACs) 140 a, 140 band 140 c respectively. There is one DAC 140 for each probe tip control.The DACs share a clock signal 142 provided by clock generator 143 thatensures the scan waveforms remain synchronized. The DACs also share asynchronization pulse 144 provided by sync generator 145 that ensuresthat the scanning starts at the same time. The DACs drive controlelectronics 146 a, 146 b and 146 c. Control electronics for SPMoperation are well known to one skilled in the art. There is onecomplete, independent set of control electronics for each probe. Thecontrol electronics are each connected to an AFM head 148 a, 148 b and148 c respectively. Each AFM head contains a 3-axis actuator 150, afeedback position sensor 152 and a deflection sensor 154. The 3-axisactuator provides for scanning along the sample 110. The feedbackposition sensor 152 in conjunction with the control electronics providecalibrated scanning. The deflection sensor 154 in conjunction with1-axis of the 3-axis actuator provides for constant force AFM scanning.This system may also be operated without force feedback, where thedeflection sensor is used to generate the scan image. There is onecomplete, independent AFM head for each feature of interest for whichsimultaneous probing is desired. Attached to the AFM heads are thecantilever 156 and scanning probe tips 114. In the embodiment shown, theAFM heads are able to position multiple scanning probe tips in closeproximity to one another. The control electronics generate the imagedata 157. The image data is passed to the analog to digital converters(ADCs) 158. The ADCs convert the image data to digital format pass theimage to the computer. The computer can then display the image data tothe user on the computer screen.

FIG. 5 b shows a detailed side view of an embodiment of the probe tipemployed with the present invention attached to a cantilever. In thisembodiment the deflection sensor uses the reflective back of thecantilever to determine the deflection of the cantilever. Thearrangement of the probe tip and cantilever shown allows the greatestclearance between multiple probes operating in close proximity. Theangled attachment of the probe tip to the cantilever, or in alternativeembodiments, the angling of the cantilever attachment to the AFM, toposition the extreme end of the probe tip as far as possible from theAFM is employed to achieve this feature.

FIG. 6 is a flow chart of the mathematical operations of the software.The standard SPM scan parameters input 159 consists of X scan size 160,Y scan size 162, X resolution 164, Y resolution 166, X offset 168 and Yoffset 170 which are used by subsequent routines to create a scanwaveform for the AFM manipulating each probe tip.

The drive waveform generation routine 172 takes the SPM scan parametersinput and outputs a drive waveform 174, identified as W, that containsboth an X value output 176 and Y value output 178. In one embodiment,shown in FIG. 7 c and FIG. 7 d and described subsequently, the drivewaveform is a triangle wave with the peaks and valleys rounded off, atthe last 5 points. For this embodiment, the waveform generation isaccomplished in the following sequence. The X values of the drivewaveform are centered about the value ‘X offset’. The X values of thedrive waveform have amplitude of ‘X scan size’ divided by 2. The Xvalues of the drive waveform have the number of points per cycle equalto 2 multiplied by the value ‘X resolution’. The X values of the drivewaveform have a number of cycles equal to 2 times the value ‘Yresolution’. The Y values of the drive waveform are centered about thevalue ‘Y offset’. The Y values of the drive waveform have amplitude of‘Y scan size’ divided by 2. The Y values of the drive waveform have thenumber of points per cycle equal to 2 multiplied by the value ‘Xresolution’ multiplied by the value ‘Y resolution’. The Y values of thedrive waveform have 1 cycle. The X offset and Y offset values define thelocation of the scan area.

The code described herein to achieve the desired AFM control has beenprogrammed in existing embodiments using a LabVIEW compiler availablefrom National Instruments Corporation, 11500 N Mopac Expwy, Austin, Tex.78759-3504, as shown in Appendix A hereto which is incorporated hereinby reference.

The start point rotation routine 180 takes the drive waveform, W, andbased on desired start point input 181 rotates the X values of the drivewaveform and the Y values of the drive waveform so the X start point 182and Y start point 184 are the first points in the waveforms. Thiscalculation places the probe tips at start points 118 a, 118 b or 188 c,as described previously with respect to FIGS. 2 b and 3 b, are thelocations where the probes will begin scanning. In the start pointroutine, rotation is defined in the software-programming context; takinga 1 dimensional array of numbers, moving a section of the numbers fromthe rear to the front, and placing the numbers that use to be at thefront, at the rear. The start point rotated X value output 176′ and theY value output 178′ of the new waveform W′ 174′ are the resulting outputof the start point rotation routine.

The scan rotation routine 186 transforms the drive waveform W′ to thespatial reference frame of the individual AFM heads 148. The inputparameter platen angle R 187 for each AFM head and associated probe tip,is the angle 122 a, 122 b or 122 c of the probe tip centerline 124 a, 12b or 124 c, respectively, measured relative to the arbitrary referenceaxis 126 on the sample as described previously with respect to FIG. 4.The output result of this routine is a rotated drive waveform W″ 174″having an X value output 176″ and a Y value output 178″. For theembodiment described herein, a multiplication by a rotationtransformation matrix M 189, formed based on an angle value equal to theplaten angle R for each AFM probe tip, is performed. In scan rotationroutine, rotation is defined in the linear algebra context; to multiplyby a matrix of the form given in the scan rotation routine to rotate theinput array about the origin by the given angle.

If all rotated drive waveforms W″ as determined by interrogatory 190,have been generated. If some AFM control electronics have not beengenerated, then the process repeats itself for the next SPMstarting withthe waveform generation routine 172. Because the invention assumes morethan one AFM, the above routines will execute at least twice,corresponding to two or more AFMs. If all AFMs have generated theirrespective rotated drive waveform, W″, then waveforms aregenerated inroutine 191 to position the probe tip of each AFM at its respectivestart point. The positioning waveform is then loaded into the AFMcontrol electronics in routine 192 and each AFM movesits respectiveprobe tip to its start point. All AFM control electronics start with acommon synchronization pulse 144, so all begin at the same time. All AFMcontrol electronics also share a common clock signal 142, so they allproceed at the same rate.

Upon reaching the start points, the rotated drive waveform W″ is loadedin routine 193 to the AFM control electronics 146 a, 146 b or 146 crespectively. Then scanning routine 194 begins. All AFM controlelectronics 146 start with a common synchronization pulse 144, so allbegin at the same time. All AFM control electronics also share a commonclock signal 142, so they all proceed at the same rate.

The data from the AFM control electronics 146 is gathered in step 195and displayed as an image on the computer screen 132 to the user. Duringoperation of the scanning routine, a monitoring function 196 isconcurrently checking if the user has selected the probe button on thecomputer screen 132. If the probe button has not been selected thescanning routine continues to gather data and update the display image.Note that in the embodiment shown the probe button is a software buttonand does not have a physical location. If the user has selected theprobe button, reflected by operation 197, then the probe point routinetakes the user's probing locations input, calculates a waveform 198 tomove from the current location of the scanning probe tips to the user'sprobing locations and outputs the waveform, as reflected in routine 200,to the AFM control electronics. The scanning probe tips are moved by theAFM control electronics to the location specified by the user's probinglocation as shown in block 201. This routine is identical in function,but different in input to the start point positioning generationroutine. The input to this function is the probing point, rather thanthe start point.

FIGS. 7 a through 7 f show examples of some of the electrical signalsduring the execution of the scanning operation. FIG. 7 a is the sharedclock 142 that is used to make sure all AFMs remain synchronized. FIG. 7b shows the synchronization pulse 144 that signals for all AFMs to beginat the same time. FIG. 7 c shows the X values of the drive waveform 176generated by the waveform generation routine 172. FIG. 7 d shows the Yvalues of the drive waveform 178 also generated by the waveformgeneration routine 172. FIG. 7 e shows an example of the X values of therotated drive waveform W″ 188, for an AFM head that is rotated to anexemplary arbitrary platen angle relative to the sample 110. FIG. 7 fshows an example of the Y values of the rotated drive waveform W″ forthe AFM head. These waveforms are generated by the scan rotation routine186. Note that after the scan rotation routine 186 the rotated drivewaveform 188, W′, depend greatly on the platen angle 122.

Operation of the embodiment of the invention disclosed herein isaccomplished as follows. The system employs multiple scanning probemicroscopes. The scanning probe tips may be in close proximity to oneanother, such as a few microns to under 1 micron. Additionally, thescanning probe tips are centered in their travel, engaged on a sampleand may be able to scan an overlapping scan area. As previouslydescribed with respect to FIGS. 2 a, 2 b, 2 c, 3 a, 3 b, and 3 c, thescan area 116 contains multiple features of interest 112.

Using the computer 130 the user enters various scanning parameters suchas X scan size 160, Y scan size 162, X offset 168, Y offset 170, Xresolution 164, Y resolution 166, X start point 182, Y start point 184and platen angles for the AFM probe tips (122 a, 122 b and 122 c for thethree probe example disclosed herein).

The user tells the computer to begin scanning and the software routinerunning on the computer 130 starts the procedure illustrated in FIG. 6.The waveform generation routine 172 generates a drive waveform W, sothat each scanning probe tip will raster an area described by thescanning parameters.

The drive waveforms W are rotated by the start point rotation routine180 so that all scanning probe tips will start at the same point intheir respective drive waveforms. This will ensure that the spacingbetween the AFM probe tips 114 will be constant for the start ofscanning.

Next, the drive waveforms are rotated by the scan rotation routine 186to result in the rotated drive waveforms W″. This rotation ensures thateven though all AFM heads and their associated scanning probe tips havea different platen angle they will all scan at the same direction at thesame time and further ensures that the spacing between scanning probetips will remain substantially constant for the duration of scanning.

Next, the rotated drive waveforms W″ are loaded to the DACs 140 a, 140 band 140 c respectively. The AFMs are positioned placing the probe tipsat the start points. Once the rotated drive waveforms have been loaded,all AFM control electronics share a common clock 142. This ensures thatthe scanning probe tips will stay synchronized. Then the synchronizationcircuit issues a synchronization pulse 144, which signals all AFMcontrol electronics 146 to begin scanning. This ensures that all of theAFMs start scanning at the same time. The DACs then output theirrespective rotated drive waveform to their AFM control electronics.During scanning the scanning probe tips move in spaced relation tomaintain constant spacing to when they first started scanning. Each setof AFM control electronics controls the feedback position sensors 152and the 3-axis actuator 150 in the associated AFM head 148 to scan in acalibrated manner. Each deflection sensor 154 monitors the deflection ofthe cantilever 156 to which the scanning probe tip 114 is attached. Thisdeflection signal is returned to the SPM control electronics 146 anddisplayed to the user on the computer screen 132.

During scanning the AFM probe tips move in an identical scanningdirection 120 at all times, as shown in FIGS. 2 a -c and 3 a -c.Similarly, the starting points 118 a, 118 b and 118 c are in the samerelative location for the scan areas 116 a, 116 b and 116 c for allscanning probe tips. Additionally, the spacing between the scanningprobe tips is constant at all times.

During scanning the computer 130 gathers data from the AFM controlelectronics 146 and displays it on the computer screen 132. When theuser locates the features of interest 112 on the computer screen, he orshe can choose to probe those features. The user then selects thelocation of the features of interest to be probed as the probinglocation 196 and selects the probe button 194. Then the computer 130will calculate and output a waveform to the DACs 140 which will drivethe AFM control electronics 146, which will drive the scanning probetips to a respective point on the sample 110 corresponding to theprobing location 196. The DACs 140 will share their common clocks 142and synchronization pulse 144 as before. The DACs 140 will then drivethe AFM control electronics 146. This will cause the scanning probe tipsto move to the probing locations 196. Note that, for the first timesince scanning began, the spacing between scanning probe tips 114 is nolonger constant once the scanning probe tips 114 begin to move towardthe probing locations 196.

For an alternative embodiment of the invention with enhancefunctionality, FIG. 8 a shows the sample 110, features of interest 112 aand 112 b and an area to be avoided 198. In FIG. 8 a the scanning probetips 114 a and 114 b are positioned on the sample 110. FIG. 8 b showseach of the scanning probe tips has its own scan area 116 a and 116 b,respectively, that excludes the area to be avoided 198. In theembodiment shown, the spacing between scanning probe tips 114 a and 114b may not always be constant. In this embodiment the probes retract inZ, the out of the plane of the sample direction, to avoid the area to beavoided. Each scan area 116 has a start point 118 that is where thescanning probe tip 114 will begin. Each scanning probe tip 114 also hasa scanning direction 120. In the embodiment shown the scanningdirections 120 are substantially the same for all probe tips 114.

FIG. 9 shows in flow chart form the generation of the Z axis proberetraction waveform consistent with the area to be avoided which isoverlaid on the waveform generation for the X and Y components of theAFM motion. FIGS. 10 a, 10 b, show the waveforms of FIGS. 7 c and 7 dexpanded and truncated for clarity. FIG. 110 c show the corresponding Zaxis actuation for the avoided area associated with the X and Y motion.Referring to FIG. 9, the X and Y extents of the area to be avoided areprovided as parameter input 202 to generation routine 204 for a controlmatrix 206 for the excluded area. A simple rectangular area is shown forthe embodiment in the drawings, but is not a limitation on theinvention. For purposes of explanation the operation of only one probetip and AFM is described herein. The control electronics monitor the X/Yposition 208 of the probe tip as driven by the appropriate waveform 178for X position and 176 for Y position shown in expanded form in FIGS. 10b and 10 a respectively. If the probe tip position has entered theexclusion matrix values 210, the probe is lifted 212 by the Z axiscontrol in the AFM. The X/Y position is then monitored to determine whenthe probe tip is clear of the exclusion matrix values 214 at which timethe probe is lowered 216 to resume generation of image data.

The exclusion area is graphically demonstrated in FIG. 10 a as Yexclusion zone 218 and FIG. 10 b as X exclusion zone 220. The resultingZ axis waveform 222 shown in FIG. 10 c demonstrates the lifting of theprobe tip when in the exclusion area. FIG. 8 c shows the scanning probetips 114 positioned on the features of interest 112 and ready for an FAexperiment.

A commercially available version of an embodiment of the invention isthe Atomic Force Probe (AFP) system available from Multiprobe, Inc, 10E. Islay Street, Santa Barbara, Calif. 93101, the assignee of thepresent application. This system is capable of placing the scanningprobe tips in close proximity, being less than a few microns, as shownin FIG. 2 c or 3 c. This system has feedback position sensors 152 forthe 3-axis actuator 150 and supporting SPM control electronics 146 asshown in FIG. 5. This system also executes the software routine shown inblock diagram form in FIG. 6. For 3 scanning probe tips 114 thismicroscope performs the operation shown pictographically in FIG. 3.

An additional commercially available atomic force microscope (AFM) isthe Veeco Metrology AFM head with supporting control electronicsavailable from Veeco Metrology Group, 112 Robin Hill Road, SantaBarbara, Calif. 93117. This commercially available system does notpresently support the invention, however, this system contains theelements shown in FIG. 5. The most noteworthy of these elements are thefeedback position sensors 152 for the 3-axis actuator 150 and thesupporting AFM control electronics 146 as shown in FIG. 5. This systemalso does not have the ability to place multiple scanning probe tips inclose proximity.

Having now described the invention in detail as required by the patentstatutes, those skilled in the art will recognize modifications andsubstitutions to the specific embodiments disclosed herein. Suchmodifications are within the scope and intent of the present inventionas defined in the following claims.

1. A scanning probe microscopy system comprising: at least two scanningprobes, each probe supported by cantilever to an atomic force microscope(AFM); control means in each AFM adapted to receive motion controlsignals; means for generating a motion control signals for scandirections for a first one of the AFMs for motion to create a scan by afirst probe; means for determining offset motion control signalsresponsive to the motion control signals for a second one of the AFMsfor motion in spaced relation to the first one of the AFMs to create anoffset scan by a second probe; means for defining an area in a deviceunder test to be avoided during scan; means for generating a retractionsignal in the first one of the AFMs responsive to the area definingmeans and the generating means upon intersection of the scan and area tobe avoided; means for generating a retraction signal in the second oneof the AFMs responsive to the area defining means and the determiningmeans upon intersection of the offset scan and the area to be avoided;and, means for generating image scan data from input signals from eachprobe.
 2. A scanning probe microscopy system as defined in claim 1wherein the means for generating a retraction signal in the first andsecond AFMs include means for sensing scan position and offset scanpositions of the first and second probes respectively.
 3. A scanningprobe microscopy system as defined in claim 1 wherein the means fordetermining offset motion control signals comprises a rotational matrix.4. A scanning probe microscopy system as defined in claim 1 wherein eachprobe and the respective cantilever are oriented for placement of a tipof the probe distal the AFM.
 5. A scanning probe microscopy system asdefined in claim 1 wherein a cantilever deflection signal is monitoredand said cantilever deflection signal comprises the input signal fromeach probe to the scan image generation means.
 6. A scanning probemicroscopy system as defined in claim 1 wherein a cantilever deflectionsignal is monitored and said cantilever deflection signal providesfeedback to the AFM for constant force scanning.
 7. A method forscanning probe microscopy comprising the steps of: attaching a firstcantilever supported probe to a first AFM; attaching a second cantileversupported probe to a second AFM; determining a scan directional patternfor the first probe; determining an area to be avoided on a device undertest; calculating a control signal corresponding to the scan directionalpattern; determining a relative position of the second probe and AFM tothe first probe and AFM; calculating an offset scan control signal basedon the scan control signal and the relative position of motion of thesecond probe in spaced relation to the first probe in the firstdirectional pattern; simultaneously supplying the scan control signal tothe first AFM and the offset scan control signal to the second AFM toprovide a scan by the first AFM and an offset scan by the second AFM;applying a probe retraction signal to the first AFM when the scanintersects the area to be avoided; applying a probe retraction signal tothe second AFM when the offset scan intersects the area to be avoided;and, generating image scan data from input from the probes.
 8. A methodfor scanning probe microscopy as defined in claim 7 wherein the step ofapplying a probe retraction signal to the first AFM further comprise thesteps of: sensing position of the first probe; and, comparing positionof the first probe and the area to be avoided; and wherein the step ofapplying a probe retraction signal to the second AFM further comprisethe steps of: sensing position of the second probe; and, comparingposition of the first probe and the area to be avoided.
 9. A method forscanning probe microscopy as defined in claim 6 wherein the step ofattaching a first cantilever supported probe further comprises theinitial step of attaching a first probe and cantilever at an angle formaximum spacing of the first probe tip from the first AFM and the stepof attaching a second cantilever supported probe further comprises theinitial step of attaching a second probe and cantilever at an angle formaximum spacing of the second probe tip from the second AFM.
 10. Amethod for scanning probe microscopy as defined in claim 7 furthercomprising the steps of: monitoring a cantilever deflection signal foreach probe; and, providing the cantilever deflection signal forgeneration of the image data.
 11. A method for scanning probe microscopyas defined in claim 7 further comprising the steps of: monitoring acantilever deflection signal for each probe; and, providing thecantilever deflection signal as feedback to the AFM for the probe forconstant force scanning.